Studies such as Fluid Loss in Swimmers in Journal Of Swimming Research, Volume 11, 1996, by Peter Peaburn, et al, say that "swimmers appear to dissipate heat mainly through conduction and convection." The study also found that "if the water is warm,' (which, if you've swum continuously and rigorously in Riverton or Reiche, you know it is,) "fluid is lost through the increased role of sweating."
Essentially, what the study found is that body mass reduced significantly in the subjects of the test. The results of which "strongly suggest the importance of swimmers consuming liquid before, during, and following a swim training session."
What that means for our swimmers is that they should follow the guidelines below:
Age Group 1 and 2 swimmers should bring a water bottle to practice, and use it!
Pre-Senior and Senior swimmers should have a water bottle for practices filled with a mix of 1/4 - 1/2 energy drink and water in order to restore and replenish energy during longer workouts, as well as to hydrate.
What to Eat During Swim Competitions
USA Swimming: Nutrition in Swimming
10 Foods for Faster Swimming
8 Nutritional Recommendations for Swimmers